Research in the Sustainable Separations Lab aims at decarbonizing energy-intensive chemical separations using synthetic membranes. We seek a balance between developing new membrane materials and fabricating scalable ultra-microporous hollow fiber membranes. We are particularly interested in carbon molecular sieve (CMS) hollow fiber membranes made by pyrolysis of polymer precursor hollow fibers. They are advanced membranes with high packing efficiency and highly tunable pore structure and transport properties for diverse gas separation applications. Our current focuses are the creation of composite ultra-thin CMS hollow fiber membranes and ultra-selective CMS membranes for hydrogen and hydrocarbon separations. We are also interested in controlling high-temperature sorption, diffusion, and permeation in CMS membranes for decarbonized chemical conversion applications. Our research is funded by the National Science Foundation (NSF), the Department of Energy (DOE), and the American Chemical Society (ACS). Below you will find more detailed descriptions of our research thrusts and recent representative publications.

Ultra-selective CMS membranes for gas and vapor separations

Aromatic polyamides (aramids) are broadly used to manufacture desalination membranes; however, they are rarely considered for gas separation. Precise hydrogen sieving was achieved in ultra-microporous CMS membranes derived from an uncrosslinked aramid synthesized by stirred interfacial polymerization of diamine and mixed diacid chloride monomers. While hydrogen bonds gave the aramid precursor unattractive separation performance, they were leveraged to provide aramid-derived CMS membranes with ultrahigh H₂/CO₂ selectivity exceeding all known CMS membranes. Adsorption in aramid-derived CMS membranes suggested their ultrahigh H₂/CO₂ selectivity was attributable to diffusion selectivity above 3000. The excellent solution processability of uncrosslinked aramids allowed the fabrication of scalable CMS hollow fiber membranes. These findings open the door to a new class of highly selective CMS membranes for H₂ separation and CO₂ capture.

Representative publications:

• Iyer, G. M.; Ku, C.-E.; Zhang, C., Hyperselective carbon membranes for precise high-temperature H2 and CO2 separation. Science Advances 2025, 11 (23), eadt7512. (10.1126/sciadv.adt7512)
• Iyer, G. M.; Zhang, C., Precise Hydrogen Sieving by Carbon Molecular Sieve Membranes Derived from Solution-Processable Aromatic Polyamides. ACS Materials Letters 2023, 5 (1), 243-248. (10.1021/acsmaterialslett.2c01029)

CMS hollow fiber membrane reactors for sustainable chemical conversion

Non-oxidative alkane dehydrogenation produces alkene and hydrogen products. The current processes face three challenges: limited conversion due to thermodynamics, rapid catalyst deactivation, and CO₂ emissions from process heating. A membrane reactor (MR) has the potential to overcome the thermodynamic limit by removing H₂in situ, but both catalyst and membrane tend to deactivate quickly. A carbon membrane reactor was developed to integrates H₂-permeable CMS hollow fiber membranes and siliceous zeolite-supported metal catalysts. By lowering the reaction temperature using catalysts with a low threshold temperature and by overcoming the thermodynamic limit with CMS membranes, we achieve high conversion and catalyst stability. The electro-conductive nature of the CMS membrane enables joule heating of the reaction, reducing CO₂ emissions. We demonstrate a CMS membrane reactor with record-high stability for propylene and ethylene production, the second- and first-largest-volume chemicals used as feedstock globally.

Representative publications:

• Bhowmick, A.; Koybasi, H. H.; Ku, C.-E.; Chen, G.; Hwang, S.; Zhang, C.; Vlachos, D. G.; Liu, D., Vacuum-assisted carbon molecular sieve membrane reactor for non-oxidative ethane dehydrogenation. Chemical Engineering Journal 2025, 518, 164563. (doi.org/10.1016/j.cej.2025.164563)
• Liu, L.; Bhowmick, A.; Cheng, S.; Blazquez, B. H.; Pan, Y.; Zhang, J.; Zhang, Y.; Shu, Y.; Tran, D. T.; Luo, Y.; Ierapetritou, M.; Zhang, C.; Liu, D., Alkane dehydrogenation in scalable and electrifiable carbon membrane reactor. Cell Reports Physical Science 2023, 4 (12), 101692. (10.1016/j.xcrp.2023.101692)

Hierarchically porous membranes and sorbents for separation applications

Porous oxide hollow fiber membranes are broadly useful for filtration and chemical separation. They are traditionally formed by phase inversion-sintering above 1200 °C, which is expensive limiting their large-scale applications. Inspired by the natural wood petrification process, we created porous oxide hollow fiber membranes via petrification of polymer hollow fiber templates at a much lower temperature (600 °C). These novel petrified hollow fiber membranes reproduce the asymmetric macropore structure of their polymer hollow fiber templates, thereby allowing rejection of macromolecular solutes without a secondary coating layer. They have a unique hierarchical micro-/meso-/macroporous structure with simultaneous high surface area and large pore volume. These findings pave the way for wider applications of porous oxide membranes. More broadly, they allow simple and inexpensive control of the geometry of hierarchically porous oxides.

Representative publications:

• Liu, L.; Ku, C.-E.; Zhang, C., Petrified Hollow Fiber Membranes with Hierarchical Pores. ACS Materials Letters 2022, 4 (5), 938-943. (10.1021/acsmaterialslett.2c00063)
• Ku, C.-E.; Liu, L.; Zhang, C., Ion-Exchange Resin-Templated Carbon Capture Sorbents with Hierarchical Pores. Industrial & Engineering Chemistry Research 2024, 63 (26), 11444-11452. (doi/10.1021/acs.iecr.4c00479)